Dynamics tracks are used in physics education to investigate concepts in kinematics and dynamics, including Newton's laws. To measure the position and motion of a cart on such a track, various methods can be used including marking the motion on a ticker tape or analyzing the motion of the cart when passed through a photogate or pair of photogates.
More recently, ultrasonic sensors have been used to track such motion by generating a high frequency sound wave and listening for the echo from the cart to determine the distance to the cart. These ultrasonic sound waves are often emitted in a wide beam and therefore are subject to interference and detection of stray objects. Noisy and erratic data may result if there are too many hard reflecting surfaces in the environment or if interference is present, such as from other ultrasonic units in the classroom.